This invention relates to a speed sensor circuit which is particularly well suited for providing a speed signal representative of the speed of a vehicle.
One type of prior magnetic speed sensor for a vehicle utilizes a relatively small impedance pick-up which experiences a relatively small magnetic flux change. Because of the small flux change, this sensor gives only a relatively small output signal. Moreover, because of the small impedance pick-up significant drive current is required. Even where a pair of pick-ups are used in a differential system, appreciable drive current is needed.
Briefly, the present invention provides an improved speed circuit which may be utilized to advantage in automotive vehicle applications, such as in a vehicle speed control system. One advantage of a circuit embodying principles of the present invention is that a high degree of accuracy is obtained with relatively small amount of circuit hardware. Another advantage is that a compact pick-up device may be used. Furthermore, because only minimal drive current is required, the circuitry may be constructed from currently available microcircuit devices thereby permitting compact packaging of the electronics. The invention provides high sensitivity, and in the exemplary preferred embodiment wherein the pick-up is magnetically coupled with a transmission gear, can operated with a substantial air gap between the pick-up and the gear. Overall the invention provides a compact, economical speed sensing circuit which may be incorporated not only in an automotive vehicle, but in other applications as well where a speed signal is desired.
The foregoing features and advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which are to be considered in conjunction with the accompanying drawing wherein there is illustrated a preferred embodiment of the invention according to the best mode presently contemplated in carrying out the invention.